1. Field of the Invention
This invention relates generally to one-way pressure relief valves that are applied to packaging for products, such as coffee, and more particularly to improved pressure relief valves that have an integrated filter and which may be used with or without a wetting agent.
2. Background Art
U.S. Pat. No. 7,178,555 (Engel et al.) discloses a one-way pressure relief valve attachable to product packaging to vent pressurized gases from the packaging. In addition, one-way pressure relief valves, such as the PLITEK PLI-VALV PV-28 pressure relief valves, are applied to packaging for products, such as coffee, to allow unwanted gases to vent from the packaging while sealing out atmospheric gases. Such valves may vary in material and construction depending on the packaging application. The valves may be made, for example, of plastic or foil, and are generally self-adhering, thin, low profile designs supplied on a nontearing polyester or paper liner.
The valves are generally attached to the product package with a heat-sealed or pressure-sensitive adhesive. An adhesive on the back side of the valves may initially mount the valves on the liner. The valves are removed from the liner and the adhesive is used to attach a valve to the package.
In operation, the valves open at a target pressure and then close at a lower target pressure, the values of which are dependent on the packaging application, after pressure inside the packaging drops. The valves vent unwanted gases and seal out atmospheric gases from rigid or flexible packaging or other enclosures. One advantage of such valves is that they allow a product, such as coffee, to be packaged immediately after roasting and grinding to preserve product freshness. Such one-way pressure relief valves allow a product, such as coffee, to degas during packaging and shipping, while reducing oxidation of the product. Use of such valves permits elimination of a bulk degassing process of the product prior to packaging. This not only speeds the overall process, saving time and money, and space, but also reduces exposure of the product to oxidation. Thus the product, such as coffee, is provided to consumers at a greater level of freshness and quality.
A sealing lubricant (also known as a wetting agent) such as a silicone or graphite impregnated oil may be added between the membrane layers of the valve to wet the relevant valve surfaces to facilitate closing of the valve. Addition of a sealing lubricant to wet the relevant valve surfaces is typically done just prior to applying the valve to the packaging. In operation, the dry strap membrane of such prior art valves is permitted to flex away from an opening to vent unwanted gases within the packaging upon reaching the application-determined opening pressure. When the pressure drops to the application-determined closing pressure, the dry strap in cooperation with the sealing lubricant wetting the dry strap, flexes back toward the opening closing the valve and preventing atmospheric gases from entering the packaging.
One-way pressure relief valves including a wetting agent are excellent for their intended purpose. However, the step of lubricating the valves with a wetting agent adds time and cost and is another factor to control in the process of applying the valves. While the wetted valve is often attached to the outside of the packaging, there may be instances in which it is desirable to put the valve inside the package with the product and inclusion of a wetting agent may not be possible because the wetting agent could come into contact with the product. Accordingly, there is a need for a one-way pressure relief valve that does not require the addition of a lubricant.
There also remains a need affecting one-way pressure relief valves generally which is to protect the pressure relief valves from becoming fouled by fine particulate matter, such as particulates within the packaging to which a valve is attached. Fouling of the one-way pressure relief valve can interfere with operation of the valve and can prevent the valve from closing completely. Incomplete valve closure can allow air to enter the package damaging the product within the package. Accordingly, there is a need for a one-way pressure relief valve that prevents valve fouling and contributes to improved operation of the one-way pressure relief valve.